Abstract
This study analyzes the sample influx (samples per case file) into forensic science laboratory (FSL) and the corresponding analysis costs and uses arbitrary re-sampling plans to establish the minimum cost function. The demand for forensic analysis increased for all disciplines, especially biology/DNA between 2014 and 2015. While the average distribution of case files was about 42.5%, 40.6% and 17% for the three disciplines, the distribution of samples was rather different being 12%, 82.5% and 5.5% for samples requiring forensic biology, chemistry and toxicology analysis, respectively. Results show that most of the analysis workload was on forensic chemistry analysis. The cost of analysis for case files and the corresponding sample influx varied in the ratio of 35:6:1 and 28:12:1 for forensic chemistry, biology/DNA and toxicology for year 2014 for 2015, respectively. In the two consecutive years, the cost for forensic chemistry analysis was comparatively very high, necessitating re-sampling. The time series of sample influx in all disciplines are strongly stochastic, with higher magnitude for chemistry, biology/DNA and toxicology, in this order. The PDFs of sample influx data are highly skewed to the right, especially forensic toxicology and biology/DNA with peaks at 1 and 3 samples per case file. The arbitrary re-sampling plans were best suited to forensic chemistry case files (where re-sampling conditions apply). The locus of arbitrary number of samples to take from the submitted forensic samples was used to establish the minimum and scientifically acceptable samples by applying minimization function developed in this paper. The cost minimization function was also developed based on the average cost per sample and choice of re-sampling plans depending on the range of sample influx, from which the savings were determined and maximized. Thus, the study gives a forensic scientist a business model and scientific decision making tool on minimum number of samples to analyze focusing on savings on analysis cost.
Highlights
Samples or forensic evidence is normally collected from crime scenes, victims and suspects in criminal cases and submitted to the Forensic Science Laboratory
Based on total case files received, it is evident that most case files requested biology/DNA analysis (537), forensic chemistry (511) and toxicology received the least number of case files (209) in the period of the two years
Based on the above discussion, it can be concluded that, the number of case files received into forensic chemistry and forensic biology/DNA was comparable in 2014 and 2015, the number of samples was totally different, at a ratio of 17:2:1 in 2014 and 14:2.5:1 in 2015 for forensic chemistry, forensic biology/DNA and forensic toxicology, respectively
Summary
Samples or forensic evidence is normally collected from crime scenes, victims and suspects in criminal cases and submitted to the Forensic Science Laboratory. Sample influx into the FSL is defined as number of samples per each case file, which is normally analyzed and reported as a single block submitted to clients as single report. In the FSL, because of uncertainty in search for criminals, an exceedingly large number of samples are normally received from the investigation teams, leading to high workload for analysts, extended turnaround time (TAT), increased backlogs, and increased analysis costs. Turnaround time (TAT) for FSL (as the time used to analyze a case file from the time it is received within FSL until the analysis report is released and collected by the customer/client) depends strongly on sample influx. The average time that it takes the FBI Laboratory to provide DNA testing results to contributors, for instance, is lengthy, ranging from approximately 150 days to over 600 days [1]
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